Abstract: In order to study hazard of Cryptosporidium isolated from pigs in China, pathogenicity of Cryptosporidium strain sucp in 5-day-old piglets was investigated using pathological tissuesection technique, scaning electron microscope and transmission electron microscope technique. The results suggested that piglets inoculated excreted watery diarrhea and debris of mucous membrane, then dehydrated. Prepatent was 3-5 days, duration of oocyst excretion was 33-43 days. The development stages of the parasite were detected in cecum, colon and rectum of piglets, goblet cell proliferated and inflammation cells infiltrated in these sites. Microvilli in colon and rectum were in atrophy, lodging and shelling. It was concluded that 5-day-old piglets were moderately affected by Cryptosporidium strain sucp.